提出利用两个深空航天器的通用测控信号进行多频点同波束干涉测量,实现两航天器的高精度相对测量。对差分相位时延进行理论推导,提出了一种针对两航天器测控信号主载波存在频差情况下的差分时延观测量误差的模型修正方法,并对月球轨道上两航天器间同波束干涉测量地面跟踪测量条件进行了分析。仿真结果表明,利用两航天器的通用测控信号进行多频点同波束干涉测量,经误差模型修正后获取了误差小于皮秒量级的差分相位时延,能为深空航天器间相对导航定位提供高精度的观测量信息。

This paper reports measurement results of the antenna phase patterns onboard flying spin satellites during the SELENE (KAGUYA) mission period, and shows monthly variations clearly for the first time. When an antenna is loaded on a spin satellite, due to the effects of the antenna phase patterns, periodical components with the spin frequency f(s) and higher order harmonics occur and influence Doppler measurements. Because Rstar and Vstar, two subsatellites of SELENE, have octagonal prismatic bodies, the 8th, 16th, and 24th harmonics are relatively stronger than the other ones in the 2-way and 4-way Doppler data. These three harmonics' amplitudes over the entire mission longer than one year clearly varied with a period of 27.32 days (one sidereal month). The antenna phase patterns were estimated using 1-26th harmonics, whose rms variations were also with a period of 27.32 days. From the 24th harmonic and the antenna phase patterns, the spin frequency variations of Rstar and Vstar over the entire mission were estimated with an accuracy of 10(-5) Hz.

Radio waves emitted from two or more landing units on the lunar surface are received by an antenna at the Earth station, and the range differences between these landing units are measured with an error of several millimeters. The phase differences between the oscillators of these landing units are monitored via an orbiter that orbits around the Moon. We have developed a simple roundtrip method to obtain these phase differences and also propose a method of calibrating the system delay on the ground. In order to observe the rotation of the Moon and monitor the phase differences effectively, we designed the position of the landing units and the orbit of the orbiter. Further, we concurrently analyzed the characteristics of the common view period. The error of the system was analyzed and to have a high accuracy. The results show that inverse VLBI technology can be used to measure the rotation of the Moon and new scientific results can be obtained.

When only data transmission signals with a bandwidth of 1 MHz exist in the rover, the position can be obtained using the differential group delay data of the same-beam very long baseline interferometry (VLBI). The relative position between a lunar rover and a lander can be determined with an error of several hundreds of meters. When the guidance information of the rover is used to determine relative position, the rover’s wheel skid behavior and integral movement may influence the accuracy of the determined position. This paper proposes a new method for accurately determining relative position. The differential group delay and biased differential phase delay are obtained from the same-beam VLBI observation, while the modified biased differential phase delay is obtained using the statistic mean value of the differential group delay and the biased phase delay as basis. The small bias in the modified biased phase delay is estimated together with other parameters when the relative position of the rover is calculated. The effectiveness of the proposed method is confirmed using the same-beam VLBI observation data of SELENE. The radio sources onboard the rover and the lander are designed for same-beam VLBI observations. The results of the simulations of the differential delay of the same-beam VLBI observation between the rover and the lander show that the differential delay is sensitive to relative position. An approach to solving the relative position and a strategy for tracking are also introduced. When the lunar topography data near the rover are used and the observations are scheduled properly, the determined relative position of the rover may be nearly as accurate as that solved using differential phase delay data.

Interferometry measurement technology is an important method for obtaining high precision navigation information in deep space exploration. This paper describes the principle of connected interferometry measurement and the signal processing method using bandwidth synthesis technology which is utilized for accurately extracting delay related to spacecraft angle location information. Meanwhile, a connected interferometry measurement experiment system is established to sample real geosychronous satellite signal for interferometry measurement analysis in Beijing Aerospace Control Center. Finally, clear fringes and high precision delay are obtained by simulation and actual experiments, ns precision is reached, these results confirm the perfect performance of connected interferometry measurement signal processing method.

The paper focuses on verifying the differential phase delay model and detecting and correcting the cycle ambiguity existed in the differential phase delay data of same-beam VLBI. We confirmed the methods of calculating the phase delay closure and the differential phase delay closure with the same wave front. We used the method to analyze the differential phase delay data of the same-beam VLBI from SELENE project. The result of the differential phase delay closure was less than several picoseconds. The method can be used to verify the same wave front differential phase delay model and to detect and correct the cycle ambiguity existed in the differential phase delay data. It can also be used to monitor the fluctuations of the differential phase delay. These results are very useful to select the data for science research and to process same-beam VLBI data in real-time for navigation.

多频点同波束VLBI技术即用射电望远镜的主波束同时观测角距很小的两个探测器,据此得到两个探测器在两个测站间的误差为皮秒量级的差分相位时延.作为同波束VLBl基本观测量的差分相位时延从本质上来说反映了两个探测器在天球上的角距信息.利用我国4个VLBI测站得到的差分相位时延数据,可实现月球车和着陆器在3.8x105km处的天球切平面上的2维精密相对定位,其相对定位误差应优于1 m.在得到误差10 m的着陆区月面地形图后,利用多频点同波束VLBI差分相位时延和着陆器测距数据,有望实现误差10 m的月球车在月面上的精密相对定位.

Multi-frequency same-beam VLBI means that two explorers with a small separation angle are simultaneously observed with the main beam of receiving antennas. In the same-beam VLBI, the differential phase delay between two explorers and two receiving telescopes can be obtained with a small error of several picoseconds. The differential phase delay, as the observable of the same-beam VLBI, gives the separation angular information of the two explorers in the celestial sphere. The two-dimensional relative position on the plane-of-sky can thus be precisely determined with an error of less than 1 m for a distance of 3.8×105 km far away from the earth, by using the differential phase delay obtained with the four Chinese VLBI stations. The relative position of a lunar rover on the lunar surface can be determined with an error of 10 m by using the differential phase delay data and the range data for the lander when the lunar topography near the rover and the lander can be determined with an error of 10 m.

Same-beam VLBI means that two spacecrafts with small separation angles that transmit multi-frequency signals specially designed are observed simultaneously through the main beam of receiving antennas. In same-beam VLBI, the differential phase delay between the two spacecrafts and the two receiving antennas can be obtained within a small error of several picoseconds. As a successful application, the short-arc orbit determination of several hours for Rstar and Vstar, which are two small sub-spacecrafts of SELENE, has been much improved by using the same-beam VLBI data together with the Doppler and range data. The long-arc orbit determination of several days has also been accomplished within an error of about 10 m with the same-beam VLBI data incorporated. These results show the value of the same-beam VLBI for the orbit determination of multi-spacecrafts. This paper introduces the same-beam VLBI and Doppler observations of SELENE and the orbit determination results. In addition, this paper introduces how to use the same-beam VLBI for a lunar sample-return mission, which usually consists of an orbiter, a lander and a return unit. The paper also offers the design for the onboard radio sources in the lunar sample-return mission, and introduces applications of S-band multi-frequency same-beam VLBI in lunar gravity exploration and applications during all stages in the position/orbit determinations such as orbiting, landing, sampling, ascending, and docking.

同波束VLBI即用射电望远镜的主波束同时观测角距很小的两个探测器发出的巧妙配置的多频点信标,据此得到两探测器在两个测站间的误差为皮秒量级的差分相位时延.在月球卫星SELENE的两个小卫星Rstar和Vstar的测定轨中,利用40多分钟的同波束VLBI和测速测距数据数小时的短弧定轨精度已显著提高,而一年多的定轨结果表明弧长数天的长弧定轨精度已达10m左右,充分证明了同波束VLBI在多目标卫星精密测定轨中的作用.本文在介绍SELENE同波束VLBI观测、多普勒数据处理和定轨结果的基础上,以用于月球采样返回探测任务中的多目标探测器如轨道器、着陆器和返回器为例,给出各探测器搭载电波源的信标设计方案及设计原则,并分析S频段多频点同波束VLBI技术在轨道器和着陆器绕月飞行、着陆器月球软着陆、着陆器月球采样、返回器从月面上升、返回器多次变轨、特别是轨道器和返回器交会对接等各个测控段的高精度测定轨或测定位及月球重力场探测中的应用.

Japanese lunar explorer SELENE (KAGUYA) was equipped with 14 instruments for various measurements of the Moon. Three of these instruments took geodetic measurements of the Moon. These were two sub-satellites and a laser altimeter. The main results obtained by the instruments are: (1) precise orbit determination with an accuracy of ten meters by Doppler and same-beam VLBI; (2) the first precise gravity fields on the lunar far side by 4-way Doppler measurements; (3) the first topography in latitudes higher than 86 degrees; (4) a global map of the gravity anomaly by using the global topography and the global gravity fields; (5) a global map of the lunar crustal thickness and (6) an illumination rate map in the north and south polar regions.

日本探月卫星SELENE(KAGUYA)携带了14种仪器设备用于对月球进行多方面的测量,其中的3种设备用于对月球进行大地测量观测.这包括两个子卫星和一台激光高度计测量设备.这些设备所获得的科学成果主要包括:利用多普勒和同波束VLBI测量得到了精度为10 m的精密轨道确定结果;利用四程多普勒测量首次获得了月球背面精确的重力场;首次获得了纬度高于86°区域的月面地形图;通过使用月球全球地形信息与月球全球重力场信息得到了全球重力异常分布图;获得了月壳厚度全球分布图以及月球南北极区光照率图.这些成果的取得进一步加深了人类对于月球的认识.

The Shanghai FEL User Facility (SFEL) for interdisciplinary studies is based on a rf linear accelerator. The prime goal of SFEL is to provide a broadly tunable laser beam from near-Ill to far-lit with tens of MW at peak power. A linear accelerator will operate in three modes: ~ 3 MeV mode, 20 ~ 30 McV mode and 40 ~ 50 MeV mode. In 20 ~ 30 MeV mode, the accelerator consists of a ns grid gun driven at 476 MHz, a 476 MHz subharmonic buncher, a 2856 MHz T-W type of bunchcr with high field gradients, and a SLAC type linac.